This invention is directed to cooling systems for performing a cryosurgical procedure. More particularly, the present invention pertains to cooling systems that use thermally insulated cryogen containers that are connectable to a cryoprobe for freezing biological tissues to cryogenic temperatures. The present invention is particularly, but not exclusively, useful for a cooling system wherein a liquid refrigerant remains in a liquid state as it flows through the system between the cryogenic container and the cryoprobe tip.
Various cryoprobes have small shapes and sizes to achieve selective cooling of biological tissues. Cooling is provided from a part of the cryoprobe (e.g., the cryoprobe tip) that will be in direct thermal contact with the target biological tissue to be treated. For many cryogenic treatment applications, temperatures below −90° C. are desirable, but certain applications will be at warmer temperatures up to 0° C.
Various liquid refrigerants such as nitrogen, argon, nitrous oxide, carbon dioxide, various hydro/fluorocarbons, and others have been tried for cryogenic treatment applications. Liquid nitrogen has a very desirable low temperature of approximately −200° C., but when it is introduced into the freezing zone of the cryoprobe, where it is in thermal contact with surrounding warm biological tissues, its temperature increases above the boiling temperature (−196° C.). Thus, it evaporates and expands several hundred-fold in volume at atmospheric pressure, and rapidly absorbs heat from the probe tip. This enormous increase in volume results in a “vapor lock” effect when the mini-needle of the cryoprobe gets “clogged” by the gaseous nitrogen.
Several liquid nitrogen cooling systems have been proposed. For example, improved cryosurgical systems for supplying liquid nitrogen to a cryoprobe tip are disclosed in U.S. Pat. No. 5,520,682 and U.S. Pat. No. 7,192,426, both of which are issued to Baust et al. Further, a system for the direct and/or indirect delivery of liquid nitrogen to a cryoprobe tip is disclosed in U.S. Pat. No. 5,334,181 which is issued to Rubinsky et al. For these and other similar type systems, cryosurgical practice shows that current cooling systems that are based on the use of liquid nitrogen as a means to cool a miniature cryoprobe tip are not practicably feasible. In large part, this is due to the rapid transition of the liquid nitrogen into the gaseous state followed by an inevitable “vapor lock”.
A Single Phase Liquid Cooling System (SPLCS) for performing a cryosurgical procedure with a cryoprobe that maintains a liquid refrigerant in its liquid state as it flows through the system even while in contact with warm biological tissues is described in patent application Ser. No. 12/425,938 to Babkin et al., filed Apr. 17, 2009, and entitled “Method and System for Cryoablation Treatment” and incorporated herein by reference in its entirety. The system described in the Babkin Application avoids the vapor lock problem. However, it describes a sophisticated flowpath from a cryogen source to the cryosurgical device including passage through a cryogenic refrigerator.
Notwithstanding the above, an improved cryosurgical cooling system is still desired.